82 M. Brochant on the 



I had already every reason to suppose that the gypsum 

 was of a formation posterior, both to the rocks of the two 

 sides, and to the opening of the valley of which it appeared 

 to fill the bottom. 



I continued to ascend, and after having traversed the 

 woods, where some projecting rocks shewed me mica slate 

 but never gypsum, I arrived at the inclined high pastures, 

 from whence I gained the foot of the upper escarpments of 

 mica slate. 



The stratification was perfectly regular ; the beds have a 

 direction nearly E. and W. and dip at 50* towards the N. ; 

 that is towards the commencement of the valley : it ap- 

 peared to be the same on the opposite mountains j of this I 

 have since assured myself. 



From the inclination and direction of the beds, it was 

 evident, that if the gypsum below was of the same forma- 

 tion as the mica slate, I ought, while crossing all the edges 

 on the summits, to meet with at least some one of gypsum. 



For this purpose, I began by retrograding to the anterior 

 part of the mountain, towards the leventine valley, and as- 

 cending it, traversed for three hours the whole of the crest. 

 It was in vain that I searched for gypsum ; there was not 

 the slightest trace of it. I once thought I had met with it, 

 observing from a distance a bed of tolerably pure white ; 

 but on visiting it, I found it was formed of a decomposed 

 dolomite.* 



I have some reason to suppose that this bed of white do- 

 lomite, which is seen from a distance, has been taken for 

 gypsum. The annexed design (Plate 2), representing 

 the plan and sections of the valley, the disposition of the 

 mica slate beds, and that of the mass of gypsum, will I 

 think shew, in an evident manner, the impossibility of ad- 

 mitting the identical formation of these two rocks. 



It is possible that some rock may have been found sub- 

 ordinate to the gypsum ; but after consulting all the authors 



* It dissolves in heated . nitric acid, and leaves a residue of plates of 

 talc. - I have even- determined by means of a rigorous analysis, the t&tal 

 absence of gypsum. 



